1. Field of the Invention
This invention relates generally to methods and apparatus for sealing a chamber and more particularly for providing a door mechanism that is intrinsically safe and capable of withstanding high pressures within a chamber.
2. Description of the Related Art
High pressure processing of semiconductor substrates is taking on greater importance because of the advent of new formulations for inter-layer dielectrics (ILD). Other technological trends, such as the reduction in size of various interconnect features, are also hastening the move to non-conventional process technologies such as high pressure. Some of these newer ILD materials are incompatible with traditional methods for removal of photoresist and post-etch residue. Conventional methods of removing photorersist, such as the use of plasma processes, cause damage to the ILD. Plasma processes, typically employing the excitation of oxidizing species such as oxygen and fluorine-containing gases using Radio Frequency (RF) or microwave (MW) energy may not distinguish between the photoresist and the underlying ILD. This is especially true of organic and organosilicate glass materials such as Dow Chemical's SILK™, Novellus Systems' CORAL™, Applied Materials' BLACK DIAMOND™, etc.
Plasma processes damage these ILD materials by either etching them and causing loss of critical dimensions, or by chemically altering them and causing an increase in their capacitance. Wet processes such as the use of solvents like N-methyl pyrilidone (NMP), hydroxylamines, etc. are limited by their ability to wet ever-decreasing feature sizes. As feature sizes shrink below 100 nm, the ability to get active chemicals into features such as vias and trenches becomes limited by surface tension. Wet processes are also not desirable for porous ILD materials. Absorption of water and other solvents in the pores of the ILD could result in the increase of capacitance. As an example of high pressure process, super critical carbon dioxide is being used for removal of photoresist and post etch residue from some of the newer ILD formulations. With super critical carbon dioxide processing, the chamber can achieve an internal pressure up to 5000 pounds per square inch (psi). The processing capability of super critical carbon dioxide is augmented by the addition of small quantities of chemical additives. These additives enhance solubility of photorersist and post etch-residue in the super critical carbon dioxide or provide reactivity necessary to break up polymeric or other chemical bonds in the residue. Of course, the use of high pressure brings with it safety concerns. For example, any leaks from the chamber may lead to emissions of the additive chemicals into the environment outside the chamber. An additional source of concern is the high stresses to which the components of the process chamber are subjected. Proper design of the wafer load port or door is necessary to prevent leakage of process fluid and mechanical failure of the door itself.
At the same time, the semiconductor industry is moving to processing single wafers as opposed to batch processing. As the transition from 200 mm substrates to 300 mm substrates becomes more pervasive, the movement to processing single wafers accelerates further.
The combination of these two trends requires development of single-substrate high-pressure chambers. As part of these chamber designs, there must be a port for loading the substrate into the chamber for processing. A great deal of consideration must be given to design of these ports and to the door mechanism that seals the port during processing. The door must have the capability of both sealing against leakage of process fluids under large internal chamber pressures (up to 5000 psi) and be sufficiently strong to withstand the high mechanical stresses imposed by such large operating pressures. Additionally, the door must be reliable enough to withstand the repeated pressurizing and de-pressurizing associated with processing single wafers.
Since most semiconductor processing chambers work at atmospheric pressure or below, door safety is not of consequence. Moreover, for vacuum chambers an external door is the preferred design since the higher external pressure enhances door sealing by exerting a force on the door against its seal. While an external door may work well for a vacuum chamber, they suffer from several disadvantages in a high pressure environment. For example, since the force due to the internal chamber pressure is working against the seal that the external door makes with the chamber, the structure to hold the door securely against the seal at high pressures has to be fairly massive. Accordingly, an externally sealed door with the attendant need for massive actuation and sealing components takes up more space. This increases the substrate-handling robot's reach requirements. Moreover, provision of these actuation components complicates the design of external exhaust ducts and hoods necessary to capture fugitive emissions from an open door or to account for the failure of a door seal during processing.
U.S. Pat. No. 6,228,563 to Starov et al. describes such an external door mechanism for a high pressure chamber. The location and size of the external door mechanism is also shown therein. The shortcomings of such an approach are evident from the massive and complicated actuation mechanisms necessary to restrain and support the door against an internal chamber pressure. Other mechanisms for removing the door from the axis of substrate motion are also necessary. Additionally, the substrate load ports must make allowance for partial insertion of the thick portion of a substrate-handling robot's end effector. This allowance increases the area over which the internal chamber pressure may act on an external door.
U.S. Pat. No. 5,857,368 to Grunes et al and U.S. Pat. No. 5,518,771 to Jeffryes et al. describe another means of accessing the interior of a high-pressure semiconductor processing chamber. Hydraulic presses are employed to move the upper and lower chamber halves away from each other to create an opening through which a semiconductor substrate may be introduced into a process cavity. Because the same mechanisms that move the chamber halves away from each other also have to support the large internal load generated by process pressure, these mechanisms are massive. Movement of large components involves overcoming large inertial forces and can lengthen the time necessary to remove a processed substrate and replace it with an unprocessed substrate, which in turn decreases throughput.
As a result, there is a need to solve the problems of the prior art to provide an intrinsically safe and robust door capable of handling high pressure semiconductor processing.